Ultra-broadband and ultra-narrowband actively tunable VO₂ metamaterial perfect absorber

To solve the problems of single absorption function and the complex structure of terahertz absorbers, this study proposes a terahertz (THz) absorber based on vanadium dioxide (VO₂) driven by electric dipole resonance, which can achieve wideband and narrowband absorption conversion. Simulation results indicate that in the narrowband absorption mode, two narrowband absorption peaks were observed at 14.6 THz and 16.8 THz respectively, and the maximum absorption exceeds 99% at the 14.6 THz frequency. In the broadband absorption mode, the absorber achieves a perfect absorption bandwidth (≥99%) of 4.6 THz, while the bandwidth with absorption exceeding 90% extends to 6.9 THz. The average absorption within the 6.9 THz range is approximately 98.29%. The investigation demonstrated that the perfect absorption effect originates from polarization resonance along with surface plasmon excitation on the VO₂ surface under the impact of incident waves. Additionally, the symmetric design of our absorber ensures polarization insensitivity under normal incidence conditions and maintains excellent absorption performance over a wide range of incident angles. Following an analysis of the impact of the air refractive index on the absorber, our findings reveal that the absorber demonstrates both high refractive index sensitivity and remarkable tuning capabilities. This design has broad application prospects and can be utilized in thermal absorbers, terahertz sensors, and detectors.